Method for preparing a farnesoid x receptor agonist

ABSTRACT

The invention relates to a process for preparing a compound of formula (I) 
     
       
         
         
             
             
         
       
     
     in particular obeticholic acid and intermediates suitable for its synthesis.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. Ser. No. 16/090,853, dated Oct.3, 2018, which is a 35 U.S.C. 371 National Phase Entry Application fromPCT/EP2017/057868, filed Apr. 3, 2017, which claims the benefit ofItalian Patent Application Nos. 102016000034216 filed Apr. 4, 2016 and102016000115948 filed on Nov. 16, 2016, the disclosures of which areincorporated herein in their entirety by reference.

FIELD OF THE INVENTION

The present invention relates to hyodeoxycholic acid and itsintermediates, in particular to their use in a process for preparingobeticholic acid.

STATE OF THE ART

6α-Ethyl-3α,7α-dihydroxy-5β-cholan-24-oic acid, also known as6α-ethyl-chenodeoxycholic acid, obeticholic acid or as 6-ECDCA, havingformula (Ia),

is an agonist of the farnesoid X receptor (FXR) and is in thepre-registration phase as active pharmaceutical ingredient for thetreatment of various forms of hepatic cirrhosis, comprisingnon-alcoholic steatohepatitis. Obeticholic acid is known from EP 1 392714, which describes its preparation starting from chenodeoxycholic acidof formula 2 according to the Scheme 1 reported below:

The synthesis for preparing obeticholic acid (Ia) starts fromchenodeoxycholic acid of formula 2, which is an extensively used productby the pharmaceutical industry and which in turn is obtained from cholicacid, a major compound of the biliary acid mixture in bovine bile. Thealkylation reaction of the anion of the protected ketone 3, prepared at−78° C. with BuLi, with EtBr to give the alkylated intermediate 4,represents the key step of the process. The yields of this step are low;the reaction conditions are not suitable for a process on an industrialscale and the synthesis is of limited efficiency. Subsequently, a newsynthesis for preparing obeticholic acid was described in EP 1 888 614.The process as described in Scheme 2 consists in the conversion ofcompound 5 into the protected silyl ether 6. The preparation of thesilyl ether is carried out by treating compound 5 with trimethylsilylchloride at −78° C. using lithium diisopropylamide as base.Subsequently, the reaction of the silyl ether 6 and acetaldehyde inpresence of BF₃·Et₂O as Lewis acid provides the α,β-unsaturated ketone 7in good yields. Hydrogenation of the double bond of 7 leads then to theketone 8, which once reduced and hydrolyzed provides obeticholic acid offormula (Ia). This process, which starts as the previous one fromchenodeoxycholic acid 2 and which is definitely more efficient than theprevious one in respect to the yields, still suffers from the use ofexpensive bases prepared by using organolithium derivatives at lowtemperatures.

In addition, the authors of J. Med. Chem 2012, 55, 84-93 underlineddifferent problems of epimerization of the carbon atom adjacent to thealkyl group of intermediate 8 during the reduction/alkaline hydrolysisof the methyl ester, while trying to repeat said process. For thisreason, they suggested to substitute the methyl ester with the benzylone and to revert the sequence of hydrogenation and reduction (Scheme3).

In this way, the reduction of the α,β-unsaturated ketone 10, obtainedstarting from chenodeoxycholic acid 2 in the same manner as alreadydescribed for compound 7, results in the protected allylic alcohol 11,which submitted to hydrogenation provides in a single step obeticholicacid (Ia) without any issue of epimerization. This optimized synthesisof obeticholic acid of formula (Ia) starting from chenodeoxycholic acid2 is more efficient than all the previous ones, but it still suffersfrom the use of expensive bases employed at low temperatures forpreparing the silyl ether derivative, but in particular, as for theother synthetic processes, for the use of chenodeoxycholic acid 2 asstarting material.

The above disclosed methods for preparing obeticholic acid of formula(Ia) have in common the problem to use the same starting material ofanimal or vegetable origin: chenodeoxycholic acid 2 is already used inthe synthesis of further active pharmaceutical ingredients present onthe market, and the availability of which, already difficult as such,may become much more difficult or even impossible in future.

In effect, chenodeoxycholic acid 2 is obtained industrially from cholicacid extracted from bovine bile. Its availability is limited by thenumber of the butchered bovines and because cholic acid is just afraction of the bovine bile. Furthermore, it is already widely used forthe preparation of ursodeoxycholic acid. Ursodeoxycholic acid is themost known first line drug for the treatment of primary biliarycirrhosis in the world.

CN 105777835, published on Jul. 20, 2016, that is after the prioritydate of Apr. 4, 2016 of the present application, discloses a furtherprocess for preparing obeticholic acid of formula (Ia) starting from6-oxo-chenodeoxycholic acid alkyl ester 12. Wittig reaction withethyltriphenylphosphonium salt in presence of a base provides the6-ethylidene chenodeoxycholic acid alkyl ester 13, which oncehydrogenated and deprotected gives obeticholic acid of formula (Ia)(Scheme 4):

6-oxo-chenodeoxycholic acid methyl ester 12 can be prepared startingfrom hyodeoxycholic acid of formula (II) as described in J. Chem. Soc.Perkin Trans 1, 1990, pages 1-3.

The inventors of the present invention repeated several times the Wittigreaction of a compound of formula 12 with a phosphonium ylide asdisclosed in CN 105777835, but they were not able to obtain the6-ethylidene chenodeoxycholic acid alkyl ester of formula 13.

By considering in details the CN 105777835 procedure, it can be notedthat the phosphonium ylide used in CN 105777835 is both a strong baseand a nucleophile. Thus, in the specific process of CN 105777835, asconfirmed by the experiments carried out by inventors of the presentinvention, the phosphonium ylide does not react with the carbonyl group,but likely just deprotonates the hydroxyls at positions C-3 and/or C-7.

Thus, it can be safely concluded that the procedures disclosed in CN105777835 are not enabling.

Thus, there is still a need to have an efficient and economic processfor the preparation of obeticholic acid of formula (Ia), which overcomesthe drawbacks of the processes known in the art and which can be easilycarried out on an industrial scale. Such process should not make use ofnatural starting materials used in the synthesis of other activeingredients, nor of reaction conditions or reagents, which are hardlycompatible with synthetic processes on an industrial level.

SUMMARY OF THE INENTION

The present invention is directed to the use of hyodeoxycholic acid offormula (II) for preparing obeticholic acid of formula (Ia). The processdemonstrates to be particularly advantageous for an industrialapplication, since hyodeoxycholic acid of formula (II) is a wasteproduct in the workup of swine bile.

DETAILED DESCRIPTION OF THE INVENTION

The inventors of the present invention have found a new and efficientmethod for preparing a compound of formula (I), in particularobeticholic acid of formula (Ia), as herein defined. This method is ofparticular advantage on an industrial scale, which as described belowovercomes the synthetic drawbacks of the prior art and in particularmakes use of a raw material of animal origin, hyodeoxycholic acid offormula (II), which today is considered only a waste product derivedfrom the workup of swine bile. Thus, the new method for preparingobeticholic acid of formula (Ia) is not solely an alternative processfor obtaining it, but, making use of a waste product, represents aconsiderable progress in the industrial field.

The invention provides as a first object a method for the preparation ofa compound of formula (I), wherein the proton in H-5 can be inconfiguration 5α or 5β or a mixture thereof, preferably obeticholic acidof formula (Ia), wherein the proton in H-5 is in configuration 5β,

by a process comprising the use of 3α,6α-dihydroxy-5β-cholan-24-oic acidof formula (II), also known as hyodeoxycholic acid, as startingmaterial,

Hyodeoxycholic acid of formula (II) is a secondary biliary acid, whichdiffers from the more famous chenodeoxycholic acid of formula 2, asdefined above in Scheme 1, because it has the hydroxylic function inposition C-6 instead of C-7 as in chenodeoxycholic acid of formula 2.Hyodeoxycholic acid is present in the bile of mammals in varyingproportions, but it is the main constituent of the mixture of cholanicacids present in the swine bile, wherein it amounts almost to 40% of thetotal. In the past, it was used in the synthesis of progesterone. In the50ies of the last century, the company Jenapharm of the former EasternGermany used it as precursor for the synthesis of steroids. Recently,however, these syntheses have been abandoned and today hyodeoxycholicacid is only a waste product of the processing of porcine bile.

The authors of the present invention have surprisingly found that it ispossible to obtain a compound of formula (I), in particular obeticholicacid of formula (Ia), from hyodeoxycholic acid of formula (II), whichotherwise is a waste product, by a process which does not make use oflow temperatures nor of expensive organometallic bases.

The problem of using hyodeoxycholic acid of formula (II) for preparing acompound of formula (I), in particular obeticholic acid of formula (Ia),is that the ethyl group has to be placed in position C-6 instead of thehydroxyl group and it is necessary to oxidize selectively position C-7in such a way that a hydroxyl function is introduced in position α.

In the process of the invention, in the case it is necessary to protectthe hydroxyl function in position C-3 and/or the carboxylic acid of acompound of the present invention and/or an intermediate thereof, beforecarrying out one of the aforementioned reactions, said chemical groupcan be protected and deprotected according to known methods. A thoroughdiscussion for protection/deprotection steps is provided for example inGreene and Wuts (Greene, T. W.; Wuts, P. G. M. “Protective Groups inOrganic Synthesis”, John Wiley & Sons Inc., 1991) or in Kocienski(Kocienski, P. J. “Protecting Groups”, George Thieme Verlag, 1994). Thehydroxyl group in position C-3 can be protected as ether, for instanceas unsubstituted or substituted benzyl ether, for example asp-methoxy-benzyl ether, 3,4-dimethylbenzyl ether, benzhydryl ether; astetrahydropyranyl ether or as silyl ether, for example as trimethylsilylether, triethylsilyl ether or tert-butyl-dimethylsilyl ether; or asester, for example as formyl, acetyl, pivaloyl or benzoyl ester.Preferably, the hydroxyl group is protected as tetrahydropyranyl ether,trimethylsilyl ether or tert-butyl-dimethylsilyl ether, or as formyl,acetyl or pivaloyl ester.

Alternatively, the hydroxylic group in position C-3 can be selectivelyoxidized to a ketone with N-bromosuccinimide, and the ketone can beprotected as acyclic or cyclic ketal, for example as dimethylketal,1,3-dioxolane or 1,3-dioxanes. Once the protection in position C-3 is nolonger necessary, the ketal can be deprotected to the ketone accordingto known methods and the obtained ketone can then be reduced to thehydroxyl group with a reducing agent, for instance with a hydridereducing agent, for example NaBH₄ or LiAlH₄.

The carboxylic acid group can be protected as ester, for instance asC₁-C₆ alkyl ester, wherein the C₁-C₆ alkyl group may be optionallysubstituted by phenyl. Preferably, the carboxylic acid group isprotected as methyl, ethyl, isopropyl, tent-butyl or benzyl ester. Theprotection or deprotection of the carboxylic acid group can be carriedout according to known methods. For instance, the ester can be preparedby activation of the carboxylate with a good leaving group asexemplified in Greene and Wuts mentioned above. Removal of the ester canbe carried out according to known methods, for example cleavage of anethyl or methyl ester with an acid or base or a benzyl ester byhydrogenation.

The authors of the present invention have found that a preferred processfor preparing a compound of formula (I), in particular obeticholic acidof formula (Ia), starting from hyodeoxycholic acid of formula (II) isthat in which first the ethyl group is placed in position C-6 instead ofthe hydroxyl and then the C-7 position is selectively oxidized.

The authors of the present invention have found an even more preferredprocess for preparing a compound of formula (I), in particularobeticholic acid of formula (Ia), starting from hyodeoxycholic acid offormula (II), by a method comprising the following steps:

I) oxidation of the hydroxyl group in position C-6 of hyodeoxycholicacid of formula (II) to the ketone;

II) reaction of the obtained ketone with an ethylidene phosphorane,preferably ethylidene triphenylphosphorane; and

after said reaction with an ethylidene phosphorane,

III) oxidation in position C-7 in such a way that a hydroxyl function isintroduced in position a; or in alternative to step III)

IV) a) the allylic oxidation in position C-7 to a ketone and

b) subsequent reduction of the ketone in position C-7 to the α hydroxylwith a reducing agent, preferably with a hydride reducing agent, forexample NaBH₄ or LiAlH₄,

and wherein the hydroxyl group in position C-3 and the carboxylic acidgroup present in the compounds described in steps I)-IV) can beoptionally protected.

Oxidation of the hydroxyl group in step I) can be carried out underconditions known in the art used for the conversion of a secondaryalcohol to a ketone. For example, conditions and reagents can be thosedescribed below for step c).

The reaction of the ketone with an ethylidene phosphorane in step II)can be carried out under Wittig conditions. For example, conditions andreagents can be those described below for step d).

The oxidation in position C-7 in step III) can be carried out using anoxidizing agent in a solvent. For example, conditions and reagents canbe those described below for step f).

The allylic oxidation in position C-7 to a ketone in step IV) a) can becarried out at conditions and with reagents as those described below forstep j).

Reduction of the ketone to the a hydroxyl in step IV) b) can be carriedout with a hydride reducing agent, for example NaBH₄ or LiAlH₄, in asolvent, for example an ether.

Preferably, the reduction is carried out using NaBH₄ in a solvent, forexample a dialkyl ether or tetrahydrofuran (THF).

A further object of the present invention is hyodeoxycholic acid offormula (II) for use in a process for preparing a compound of formula(I), in particular obeticholic acid of formula (Ia).

According to the process of the invention, a key compound in thepreparation of a compound of formula (I), in particular of formula (Ia),is a compound of formula (VII)

wherein R_(a) is hydrogen or an optionally substituted linear orbranched C₁-C₆ alkyl group, or an optionally substituted aryl;

R_(b) is hydrogen and R_(c) is OH or O-PG, wherein PG is an alcoholprotecting group as defined above, for instance an unsubstituted orsubstituted benzyl ether, a tetrahydropyranyl ether, a silyl ether, oran ester; or, alternatively,

R_(b) is OR₁ and R_(c) is OR₂;

wherein each of R₁ and R₂, which may be the same or different, is aC₁-C₆ alkyl group, or R₁ and R₂ taken together form a —(CH₂)_(n)- chain,wherein n can be 2 or 3,

and wherein the symbol

indicates that the absolute configuration of the double bond can be (E)or (Z) or a mixture thereof; and wherein the H-5 proton can be either inconfiguration 5α or 5β or a mixture thereof.

Preferably, the alcohol protecting group is tetrahydropyranyl ether,trimethylsilyl ether or tert-butyl-dimethylsilyl ether, or a formyl,acetyl or pivaloyl ester.

Preferably, a compound of formula (VII) is a compound of formula (VIIa),wherein the proton H-5 is in configuration 5β,

and wherein R_(a), R_(b), R_(c) and the symbol

are as defined above.

A C₁-C₆ alkyl group, which can be linear or branched, is typically aC₁-C₄ alkyl group, for instance methyl, ethyl, propyl, isopropyl, orbutyl, isobutyl, tent-butyl, optionally substituted by one or moresubstituents, preferably from one to three substituents, which may bethe same or different, such as halogen, for example chlorine orfluorine, or aryl, for example phenyl.

An aryl group may be, for example, a phenyl or naphthyl group, typicallyphenyl. Said aryl group may be optionally substituted by one to threesubstituents independently selected from a linear or branched C₁-C₄alkyl group, which in turn may be optionally substituted by one to threehalogen atoms, typically fluorine; a hydroxy group; a C₁-C₄ alkoxygroup, for example methoxy; a halogen atom, such as bromine or chlorine;a cyano group; and a nitro group.

Preferably, the substituent R_(a) in a compound of formula (VII) or(VIIa) is H, methyl or benzyl.

According to an aspect of the invention, a compound of formula (VII), assingle isomer or as mixture of isomers, and in particular a compound offormula (VIIa), as defined above, and wherein R_(b) is OR₁ and R_(c) isOR₂ as defined above, can be obtained by a process comprising thefollowing steps:

-   a) selective oxidation of the hydroxyl group in position C-3 of a    compound of formula (III)

wherein R is an optionally substituted linear or branched C₁-C₆ alkylgroup, or an optionally substituted aryl group, to obtain a compound offormula (IV):

wherein R is as defined above;

-   b) protection of the ketone group in C-3 position of a compound of    formula (IV) to obtain a compound of formula (V):

wherein R₁, R₂ and R are as defined above;

-   c) oxidation of the hydroxyl group in position C-6 of a compound of    formula (V), and optional saponification of the ester group, to    obtain a compound of formula (VI):

wherein R_(a), R₁ and R₂ are as defined above; and

-   d) reaction of a compound of formula (VI) with a compound of formula    (VIII):

wherein Ph is phenyl, to obtain a compound of formula (VII); and inparticular a compound of formula (VIIa).

A compound of formula (III) is a known compound, or can be obtained inan advantageous manner from hyodeoxycholic acid of formula (II) by

-   e) protection of the carboxylic function of the hyodeoxycholic acid    of formula (II) in order to obtain a compound of formula (III):

wherein R is as defined above.

In step a) of the synthesis, the protected ester of hyodeoxycholic acidof formula (III) is oxidized selectively at the C-3 position providing acompound of formula (IV). The selective oxidation at the C-3 required anoptimization study. Indeed, the oxidation of the compound of formula(III) has been studied under different experimental conditions, forexample under the Swem conditions, such as DMSO activated with (COCl)₂,using KMnO₄ or TEMPO as catalyst in presence of NaClO or NaClO₂, but inall cases only mixtures of products with mono or double oxidations ofpositions C-3 and C-6 were obtained. However, it was found that it ispossible to obtain a compound of formula (IV) with high selectivitycarrying out the oxidation with N-bromosuccinimide in a solvent. Theoxidation reaction can be performed in a polar aprotic solvent selected,for example, in the group comprising dimethyl sulfoxide; acetonitrile;dimethylformamide or dimethylacetamide; a ketone, for example acetone ormethylethylketone; water; or a mixture of two or more, preferably two orthree, of said solvents.

According to a preferred aspect of the invention, the reaction can becarried out in presence of a mixture of water/acetone. Said reaction canbe performed at a temperature comprised from about −10° C. to 50° C.,preferably from about 0° C. to 10° C.

A preferred aspect of the invention is the oxidation of a compound offormula (III) with N-bromosuccinimide to obtain a compound of formula(IV).

According to step b), the ketone group at C-3 of a compound of formula(IV) is protected before oxidation at C-6.

The protection step can be performed according to known methods, forexample in presence of a C₁-C₄ alcohol, of a diol, for example ethyleneglycol or propylene glycol, or of vinyl ether and in presence of an acidcatalyst, in order to provide a protected compound of formula (V),wherein R₁ and R₂ are as defined above. Preferably, the substituents R₁and R₂ of a compound of formula (V) taken together form a —(CH₂)_(n)-chain, wherein n is 2.

According to step c), thanks to the protection of the ketone function atposition C-3, the compound of formula (V) can be thus selectivelyoxidized at C-6, with following optional saponification of the estergroup, to give a compound of formula (VI), wherein R_(a), R₁ and R₂ areas defined above.

The oxidation reaction can be carried out under conditions known in theart used for the conversion of a secondary alcohol to a ketone. Thereaction is preferably carried out at a pH value between about 4 and 10.These conditions permit to avoid the hydrolysis of the ester or acetalfunctionalities, which do occur at strongly basic or strongly acidic pHvalues. Preferably, the oxidation reaction is conducted in the presenceof the catalyst TEMPO using NaClO or NaClO₂ as oxidizing agents in asolvent.

The solvent can be a polar aprotic solvent, such as dimethylformamide,dimethylsulfoxide or acetonitrile; an ethereal solvent, for examplediethyl ether, methyl tent-butyl ether or tetrahydrofuran; a ketone, forexample methyl ethyl ketone, methyl isobutyl ketone or acetone; anapolar aprotic solvent, for example hexane, heptane, toluene or xylene;an ester, for example an acetate of a linear or branched C₁-C₅ alcohol,preferably ethyl acetate; a chlorinated solvent, such as dichloromethane(CH₂Cl₂), chloroform or chlorobenzene; or water, or an aqueous solutionof an inorganic salt able to generate a pH between about 7 and 10; or amixture of two or more, typically two or three, of the above solvents.Preferably, the solvent is a biphasic system consisting of an organicsolvent, preferably dichloromethane, and an aqueous solution at a pHbetween about 7 and 10.

The optional saponification of a compound of formula (VI) can be carriedout according known methods.

According to step d), a compound of formula (VI) can be converted into acompound of formula (VII), preferably into a compound of formula (VIIa),as defined above, for example by a process carried out under Wittigconditions using a phosphorus ylide of formula (VIII), wherein Ph isphenyl, in a solvent.

The ylide of formula (VIII) can be simply prepared by treating anethyltriphenylphosphonium salt with a strong base as well known to aperson skilled in the art.

A strong base can be for example a strong organic base, for instance analkaline metal alkoxide, preferably potassium tent-butylate or sodiumtent-butylate; NaH; or lithium diisopropylamide (LDA).

The Wittig reaction can be performed at a temperature comprising between−10° C. and the reflux temperature of the solvent, preferably betweenabout 0° C. and 30° C. During the conversion of a compound of formula(VI) into a compound of formula (VII) a partial epimerization of the C-5of a compound formula (VI) can occur in the experimental conditions ofthe Wittig reaction. A compound of formula (VIIa), wherein the protonH-5 is in configuration 5β, can be isolated for example bycrystallization, typically in a linear or branched C₁-C₅ alcohol, forinstance methanol, ethanol isopropanol, n-butanol, iso-butanol orn-pentanol, preferably isopropanol.

In step e) of the synthesis, hyodeoxycholic acid of formula (II) isconverted into a derivative with a protected carboxylic acid function,such as an ester of formula (III). Such protection can be carried outaccording to known methods in the art, for example in the field ofsteroid chemistry, by esterification of cholanic acids.

The inventors of the present invention have found that a compound offormula (VII), preferably of formula (VIIa), is a key compound for thepreparation of a compound of formula (I), and preferably of obeticholicacid of formula (Ia).

A compound of formula (VII), in particular of formula (VIIa), which arenew compounds, are further embodiments of the invention, as well as acompound of formula (VIIa) for use in a method for preparation ofobeticholic acid of formula (Ia).

A further embodiment of the present invention is a compound of (VII) orof formula (VIIa) selected from:

3-spiro[1,3]dioxolane-(6E/Z)-ethyliden-5β-cholan-24-oic acid methylester;

3-spiro[1,3]dioxolane-6-ethyliden-cholan-24-oic acid;

3-spiro[1,3]dioxolane-(6Z)-ethylidene-5β-cholan-24-oic acid methylester; and

-   -   3α-(2,2-dimethylpropanoyl)-(6Z)-ethylidene-5β-cholan-24-oic acid        methyl ester.

A compound of formula (VII), wherein R_(b) is OR₁ and R_(c) is OR₂ asdefined above, can be converted into a compound of formula (I), asdefined above, by a process further comprising:

-   f) stereoselective allylic oxidation of a compound of formula (VII)    to obtain a compound of formula (IX):

wherein R_(a), R₁ and R₂ and the symbol

are as defined above;

-   g) the removal of the protection at C-3 position of a compound of    formula (IX) to obtain a compound of formula (X):

wherein the symbol

and R_(a) are as defined above;

-   h) the stereoselective reduction of the ketone group at C-3 position    of a compound of formula (X) to obtain a compound of formula (XI):

wherein the symbol

and R_(a) are as defined above; and

-   i) the hydrogenation of a compound of formula (XI) to obtain a    compound of formula (I); or-   j) allylic oxidation in position C-7 of a compound of formula (VII)    to obtain a compound of formula (XII):

wherein the symbol

, R_(a), R₁ and R₂ are as defined above;

-   k) the removal of the protection at C-3 position of a compound of    formula (XII) to obtain a compound of formula (XIII):

wherein the symbol

and R_(a) are as defined above and optional saponification;

-   l) the hydrogenation of a compound of formula (XIII) to obtain a    compound of formula (XIV):

wherein R_(a) is as defined above; and

-   m) reduction of a compound of formula (XIV) to obtain a compound of    formula (I).

In particular, a compound of formula (VII), and preferably a compound of(VIIa), can be converted into a compound of formula (I), and preferablyinto a compound of formula (Ia), as defined above, by a process furthercomprising:

-   n) the removal of the protection at C-3 position of a compound of    formula (VII), or (VIIa), to obtain a compound of formula (XV), or    (XVa), respectively,

wherein the symbol

and R_(a) are as defined above;

-   o) the stereoselective reduction of the ketone group at the C-3    position of a compound of formula (XV), or (XVa), to obtain a    compound of formula (XVI), or (XVIa), respectively, and optional    saponification of the ester function:

wherein the symbol

and R_(a) are as defined above; and

-   p) the allylic oxidation in position C-7 in a compound of    formula (XVI) or (XVIa), and optional saponification of the ester    function, to obtain a compound of formula (XI) or (XIa),    respectively:

wherein the symbol

and R_(a) are as defined above;

-   q) the hydrogenation of a compound of formula (XI), or (XIa), to    obtain a compound of formula (I), as defined above, or obeticholic    acid of formula (Ia); or-   r) the protection of the hydroxyl group at C-3 position and allylic    oxidation of position C-7 of a compound of formula (XVI), or (XVIa),    or the allylic oxidation of position C-7 of a compound of formula    (VII), or (VIIa), and optional saponification of the ester function,    to obtain a compound of formula (XVII), or (XVIIa)

wherein the symbol

and R_(a), R_(b) and R_(c) are as defined above;

-   s) the oxidation of the hydroxyl group in position C-7 to the keto    group and the removal of the protection at C-3 of a compound of    formula (XVII) or (XVIIa) to obtain a compound of formula (XVIII) or    (XVIIIa):

wherein the symbol

and R_(a) are as defined above;

-   t) the hydrogenation and reduction of a compound of formula (XVIII)    or (XVIIIa) to obtain a compound of formula (I) or (Ia).

In a preferred aspect of the invention a compound of formula (VIIa) is akey compound in the process for preparation obeticholic acid of formula(Ia), which can be preferably obtained according to the syntheticsequence from n) to q) or r) to t).

The stereoselective allylic oxidation of a compound of formula (VII)according to step f), or of a compound of formula (XVI) or (XVIa)according to step p) or of a compound of formula (VII), (VIIa), (XVII),or (XVIIa) according to step r) can be carried out using an oxidizingagent in a solvent.

An oxidizing agent can be for example SeO₂, MnO₂ or a peroxyester, forexample tent-butyl perbenzoic acid, in presence of a Cu(I) salt or ofPd, Ru or Rh complexes, or a hydroperoxide, for example tent-butylhydroperoxide, catalyzed by Cu/Al oxides.

The allylic oxidation can be performed at a temperature comprised fromabout −10° C. to the reflux temperature of the solvent, preferablybetween about 20° C. and 80° C.

The solvent may be a polar aprotic solvent, such as dimethylformamide,dimethylsulfoxide or acetonitrile; an ethereal solvent, for examplemethyl tent-butyl ether, tetrahydrofuran or dioxane; a ketone, e.g.methyl ethyl ketone, methyl isobutyl ketone or acetone; an apolaraprotic solvent, for example hexane, heptane, toluene or xylene; anester, for example an acetate of a linear or branched C₁-C₅ alcohol,preferably ethyl acetate; a chlorinated solvent, such as dichloromethane(CH₂Cl₂), chloroform or chlorobenzene; or water; or a mixture of two ormore, typically two or three, of the above solvents.

According to step g), k) or n), the acetal protection of a compound offormula (IX), of formula (XII), of formula (VII) or of formula (VIIa)can be removed providing a compound of formula (X), of formula (XIII),of formula (XV) or of formula (XVa), respectively, wherein R_(a) is asdefined above.

The reaction can be performed in an acidic aqueous solution, accordingto methods known to the skilled person, used for the hydrolysis ofacetals

The compounds of formula (IX), (X), (XII), (XIII), (XV), (XVa), (XVI),(XVIa), (XVII), or of formula (XVIIa) are new and are a furtherembodiment of the present invention.

A further embodiment of the present invention is a compound of formula(IX), (X), (XII), (XIII), (XV), (XVa), (XVI), (XVIa), (XVII), or offormula (XVIIa), in particular a compound selected from:

3-spiro[1,3]dioxolane-6-ethyliden-7α-hydroxy-5β-cholan-24-oic acidmethyl ester;

3-oxo-6-ethylidene-5β-cholan-24-oic acid methyl ester;

3α-hydroxy-(6Z)-ethylidene-5β-cholan-24-oic acid methyl ester;

3α-(2,2-dimethylpropanoyl)-7α-hydroxy-(6E)-ethylidene-5β-cholan-24-oicacid methyl ester.

Another embodiment of the present invention is the use of a compound offormula (IX), (X), (XII), (XIII), (XV), (XVI) or (XVII) for thepreparation of a compound of formula (I) and the same compounds for theuse in a method for the preparation of a compound of formula (I).

A further embodiment of the present invention is the use of a compoundof formula (XVa), (XVIa) or (XVIIa) for the preparation of obeticholicacid of formula (Ia), and the same compound for the use in a method forthe preparation of obeticholic acid of formula (Ia).

The stereoselective reduction of the ketone group at C-3 in a compoundof formula (X), of formula (XV) or of formula (XVa) according to stepsh) or o), or of a compound of formula (XVIII) or (XVIIIa) according tosteps t) can be carried out with a hydride reducing agent, for exampleNaBH₄ or LiAlH₄, in a solvent, for example an ether. According to stepm), a compound of formula (XIV) can be reduced by a reducing stepanalogous to the ones reported in Chemistry Letters, 1996, 5, 335-336,or in Steroids, 2006, 71(6), 469-475, with a hydride reducing agent, forexample NaBH₄ or LiAlH₄, in a solvent, for example an ether, asindicated above.

Preferably, the reduction in steps h), m) or o) can be carried out usingNaBH₄ in tetrahydrofuran (THF).

The hydrogenation of a compound of formula (XI), or of formula (XIa) toobtain a compound of formula (I), in particular of obeticholic acid offormula (Ia), according to the steps i) and q), or of formula (XIII)according to the step l), or of a compound of formula (XVIII) or(XVIIIa) according to steps t) can be carried out according to knownmethods, in particular as described in J. Med. Chem 2012, 55, 84-93, ina mixture of THF/methanol using Pd/C as catalyst. Optionally, a crudeproduct of formula (XIa) as obtained after the hydrogenation can bepurified by crystallization in order to obtain pure obeticholic acid offormula (Ia). For example, hydrogenation in step l) of a compound offormula (XIII) to obtain a compound of formula (XIV), as defined above,can be performed as reported in EP 1 888 614.

The hydrogenation of a compound of formula (XI), (XIa) or (XIII) can becarried out by catalytic hydrogenation in presence of homogenous orheterogeneous metal catalyst, for example a Pd, Pt, Ni, Rh or Rucatalyst, preferably a Pd catalyst.

In case of an heterogeneous metal catalyst, the catalyst is preferablyplaced on an inert support, such as, for example, carbon, bariumhydroxide, alumina, calcium carbonate; preferably charcoal. Theconcentration of the metal on the support may vary between about 1% and30%, preferably between about 5% and 20%.

The employed hydrogen pressure may vary from about 1 atm to 40 atm,preferably from about 1 atm to 10 atm.

The molar quantity of the used catalyst, referred to a compound offormula (XIII), is comprised between about 0.1 and 10%, preferablybetween about 0.5 and 5%.

The reaction can be carried out in presence of an organic solventselected, for example, from a polar aprotic solvent, such asdimethylformamide, dimethylacetamide acetonitrile or dimethylsulfoxide;an acyclic or cyclic ethereal solvent, typically tetrahydrofuran ormethyl tent-butyl ether; a chlorinated solvent, typicallydichloromethane; an apolar aprotic solvent, for example toluene orhexane; a polar protic solvent, for example a linear or branched C₁-C₆alcohol, in particular methanol, ethanol, isopropanol or butanol; anester, for example ethyl acetate, isopropyl acetate or butyl acetate; alinear or branched C₃-C₇ ketone, for example acetone, methyl ethylketone, methyl isobutyl ketone; a carboxylic acid, for example aceticacid or propionic acid; or water; or a mixture of two or more, typicallytwo or three, of the above solvents.

Alternatively, the hydrogenation reactions can be carried out in asolution of a mineral acid or base, for example hydrochloric acid orsulfuric acid, or sodium or potassium hydroxide; or a mixture of themwith one, two or three organic solvents indicated above.

Said hydrogenation reactions can be performed at a temperature comprisedfrom about 0° C. and the reflux temperature of the solvent, preferablybetween about 25° C. and the reflux temperature.

The hydrogenation reaction of a compound of formula (XI), (XIa) or(XIII) can be carried out by a hydrogen transfer reaction, using ahomogeneous or heterogeneous metal catalyst, for example those definedabove, and a hydrogen donor. The latter can be selected for example fromthe group comprising cyclohexene; cyclohexadiene; methylcyclohexene;limonene; dipentene; menthene; hydrazine; phosphinic acid or itsderivatives, such as sodium hypophosphite; indoline; ascorbic acid;formic acid or its sodium or ammonium salts; and secondary alcohols, forexample isopropanol. A preferred hydrogen donor is ammonium formate.

The molar ratio between the hydrogen donor and the compound of formula(XIII) can be between about 1.5 and 50, preferably between about 1.5 and10.

The reduction by the hydrogen transfer reaction can be carried out inpresence of an organic solvent, selected for example from one of theabove mentioned solvents.

The allylic oxidation in position C-7 in a compound of formula (VII)according to step j) to obtain a compound of formula (XII), as definedabove, can be performed in the conditions as described for an allylicoxidation described previously, which results immediately from thealkene to the enone instead of the allylic alcohol, as described forexample in Synthesis 2013, 45, 2201-2221. Preferably, the oxidation canbe carried out using metal oxidizing systems based on Cr, Cu, Se, Rh,Co, Ru, Pd and in absence of a metallic oxidant in the presence ofNaClO, NaClO₂, NaIO₄, O₂ or an organic peroxide, for exampletert-butylhydroperoxide.

The protection of the hydroxyl group at C-3 position in step r) and theremoval of the protecting group in step s) can be performed according toknown methods. For example, the hydroxyl group can be protected as esterby reaction with an acyl chloride or anhydride in presence of a base,for example pyridine or trimethylamine (TEA). The cleavage of the estercan be performed for example by treatment with a base, for examplesodium hydroxide. Alternatively, the hydroxyl group can be protected asether by reaction with dihydropyran, unsubstituted or substituted benzylhalide or a silyl halide, wherein the halide can be chloride or bromide.The cleavage of the tetrahydropyran or the silyl ether can be performedfor example by treatment with an acid, and the benzyl protecting groupby hydrogenation.

The oxidation of the hydroxyl in position C-7 to its keto derivative ofstep s) can be performed according to known methods. For example, thehydroxyl group can oxidized with IBX or an IBX adduct, for instance asdescribed in Mendeleev Comm. 2012, 22, 129-131 or in PCT/EP2016/070883.

A further embodiment of the present invention is directed to apharmaceutical composition comprising a compound of formula (Ia), thusbeing 6α-ethyl-3α,7α-dihydroxy-5β-cholan-24-oic acid, also known as6α-ethyl-chenodeoxycholic acid, obeticholic acid or as 6-ECDCA,

and a pharmaceutically acceptable carrier, wherein the obeticholic acidof formula (Ia) does not comprise chenodeoxycholic acid of formula 2.The pharmaceutical composition can be prepared according to knownmethods.

Chenodeoxycholic acid of formula 2 and obeticholic acid of formula (Ia)have similar physicochemical properties and as asserted by Dr. MelissaRewolinski under C.F.R. § 1.132 during the prosecution of U.S. Pat. No.9,238,673 signed on Sep. 25, 2015, a separation by chromatography, evenby HPLC, would be impractical.

The process of preparing obeticholic acid of formula (Ia) according tothe present invention is consequently of particular advantage, since itdoes not make use of chenodeoxycholic acid of formula 2. Accordingly,obeticholic acid of formula (Ia), as obtained by the process of thepresent invention, is free from chenodeoxycholic acid 2. Therefore,there is no need to separate said products.

The following examples further illustrate the invention.

EXAMPLE 1 Synthesis of 3α-Oxo-6α-Hydroxy-5β-Cholan-24-Oic Acid MethylEster of Formula (IV) with R═Me

Hyodeoxycholic acid methyl ester (16.0 g, 39.4 mmol) of formula (III) isdissolved in a solution of 160 mL of acetone and 80 mL of water in a 250mL three-neck flask comprising a thermometer and a magnetic stirrer. Theobtained solution is cooled down to a temperature between 0 and 5° C.and N-bromosuccinimide (11.9 g, 67.0 mmol) is added portionwise assolid. The reaction mixture is stirred at a temperature between 0 and 5°C. for 3 hours, then treated with 5% NaOH solution (70 mL) and stirredfor an additional hour. The mixture is then concentrated under reducedpressure and extracted with toluene. The obtained organic layer is firstwashed with a 5% NaOH solution, then with a saturated solution of NaCl.The obtained organic phase is used as such in the subsequent reaction.An aliquot of the solution is concentrated to dryness and analyzed.

¹H-NMR (CDCl₃, 400 MHz, 24° C.) δ: 0.65 (3H, s); 0.89 (3H, d, J=6.4 Hz);0.97 (3H, s); 2.36-1.07 (27H, m); 3.62 (3H, s); 4.04 (1H, m).

¹³C-NMR (CDCl₃, 100 MHz, 24° C.) δ: 213.20, 174.71, 67.36, 56.08, 55.89,51.49, 50.21, 42.80, 40.19, 39.80, 37.10, 37.05, 36.13, 36.10, 35.28,34.50, 34.19, 30.99, 30.90, 28.07, 24.15, 22.82, 21.07, 18.24, 12.03.

EXAMPLE 2 Synthesis of 3-Spiro[1,3]Dioxolane-6α-Hydroxy-5β-Cholan-24-OicAcid Methyl Ester of Formula (V) with R═Me; R₁ and R₂ Taken TogetherForm a —(CH₂)_(n)-Chain, wherein n is 2.

The solution as obtained in Example 1 is treated with ethylene glycol(10.9 g, 175 mmol) and paratoluenesulfonic acid (0.0750 g, 0.395 mmol)in a 250 mL three-neck flask comprising a thermometer, a magneticstirrer and a Dean-Stark apparatus. The solution is heated to reflux toremove the water/toluene azeotrope and stirred for 2 hours. At the endof the reaction the mixture is cooled down to about 20° C. and stirredfor at least a further hour to allow the product to precipitate. Themixture is filtered off and the solid washed with water and pre-cooleddiethyl ether. Then, the solid is dried under reduced pressure to obtainthe 3-spiro[1,3]dioxolane-6α-hydroxy-5β-cholan-24-oic acid methyl esterof formula (V) (14.9 g, 33.2 mmol) with a yield of 85%, calculated fromthe hyodeoxycholic acid methyl ester of formula (III). The product isanalyzed by ¹H and ¹³C-NMR and results to be sufficiently pure to beused in the next step without any further purification.

¹H-NMR (CDCl₃, 400 MHz, 24° C.) δ: 0.63 (3H, s); 0.90 (3H, d, J=6.4 Hz);0.92 (3H, s); 1.04-2.49 (26H, m); 3.70 (3H, s); 3.94 (4H, m); 4.05 (1H,m).

¹³C-NMR (CDCl₃, 100 MHz, 24° C.) δ: 174.79, 109.71, 67.83, 64.20, 64.09,56.13, 55.86, 51.49, 47.26, 42.82, 39.91, 39.15, 35.88, 35.31, 34.63,34.58, 34.38, 31.02, 30.93, 30.13, 28.68, 28.09, 24.15, 23.25, 20.97,18.23, 12.02.

EXAMPLE 3 Synthesis of the 3-Spiro[1,3]Dioxolane-6-Oxo-5β-Cholan-24-OicAcid Methyl Ester of Formula (VI) with R_(a)═Me; R₁ and R₂ TakenTogether Form a —(CH₂)_(n)-Chain, wherein n is 2.

3-Spiro[1,3]dioxolane-6α-hydroxy-5β-cholan-24-oic acid methyl ester offormula (V), as prepared in Example 2 (14.9 g, 33.2 mmol), KBr (1.97 g,16.6 mmol), Bu₄NBr (0.640 g, 1.99 mmol), Na₂HPO₄·2H₂O (0.71 g, 4.0 mmol)and NaH₂PO₄·H₂O (0.79 g, 0.57 mmol) are dissolved in a mixture composedby CH₂Cl₂ (150 mL) and water (40 mL) in a 500 mL three-neck flaskcomprising a mechanical stirrer, thermometer and a dropping funnel. Theobtained biphasic mixture is cooled down to 0° C. and treated with TEMPO(0.16 mg, 0.99 mmol) and a 1.9% solution of NaOCl (143.0 mL, 36.49 mmol)keeping the temperature below 5° C. Once the addition is completed, thereaction mixture is stirred for 30 minutes and then treated with MeOH.After 15 minutes the organic phase is then separated and washed with asolution of 5% HCl (2×50 mL), a solution of 5% NaOH (2×50 mL) and with asaturated NaCl solution (50 mL) and finally dried over anhydrous Na₂SO₄.After filtration, the solution is concentrated under reduced pressureproviding the 3-spiro[1,3]dioxolane-6-oxo-5β-cholan-24-oic acid methylester of formula (VI) (14.5 g, 32.4 mmol) with a yield of 97%.

The product was analyzed by ¹H and ¹³C-NMR and resulted to besufficiently pure to be used in the next step without any furtherpurification.

¹H-NMR (CDCl₃, 200 MHz, 24° C.) δ: 0.71 (3H, s); 0.91 (3H, s); 0.97 (3H,d, J=6.2 Hz); 1.04-2.49 (26H, m); 3.71 (3H, s); 3.97 (4H, m).

¹³C-NMR (CDCl₃, 50 MHz, 24° C.) δ: 213.60, 174.77, 108.23, 64.68 (2C),58.73, 57.17, 56.12, 51.82, 43.44, 43.09, 39.97, 39.67, 38.23, 37.26,35.62, 34.76, 33.69, 31.38, 31.27, 30.55, 28.35, 24.30, 23.34, 21.49,18.61, 12.36.

EXAMPLE 4 Synthesis of the3-Spiro[1,3]Dioxolane-(6E/Z)-Ethyliden-5β-Cholan-24-Oic Acid MethylEster of Formula (VII) with R_(a)═Me; R₁ and R₂ Taken Together Form a—(CH₂)_(n)- Chain, Wherein n is 2.

Ethyltriphenylphosphonium bromide (10.80 g, 29.14 mmol) is suspendedunder inert atmosphere in 70 mL of anhydrous THF in a 250 mL three-neckflask comprising a dropping funnel, a thermometer and a magneticstirrer. The mixture is cooled down to 0° C., solid t-BuOK (3.20 g, 28.6mmol) is added portionwise and the mixture is stirred for 40 minutes.Then, a solution of 3-spiro[1,3]dioxolane-6-oxo-5β-cholan-24-oic acidmethyl ester of formula (VI) (5 g, 11.2 mmol), prepared as described inExample 3, in 30 mL of THF is added. The reaction mixture is stirred for18 hours and the temperature was raised within the same time to roomtemperature. At the end of the reaction the mixture is treated withwater (1.0 g, 55 mmol) and concentrated under reduced pressure. Theobtained residue is purified by silica gel chromatography(toluene/acetone 90/10), providing the3-spiro[1,3]dioxolane-(6E/Z)-ethyliden-5β-cholan-24-oic acid methylester of formula (VII) (2.82 g, 6.16 mmol) as solid amorphousdiastereoisomeric mixture (E)/(Z).

¹H-NMR (CDCl₃, 200 MHz, 24° C.) δ: (diagnostic signals, mixture E/Z)0.61-0.63 (9H, m); 0.80 (3H, m), 0.90 (6H, d, J=6.4 Hz); 1.59-1.53 (6H,m); 3.64 (6H, s); 3.92 (8H, m); 4.87 (1H, q, J=6.8 Hz), 5.18 (1H, q,J=6.6 Hz).

¹³C-NMR (CDCl₃, 50 MHz, 24° C.) δ: (mixture E/Z) 174.14, 139.13, 117.00,112.99, 109.53, 109.00, 63.87, 63.79, 56.12, 55.52, 54.42, 51.13, 48.36,43.14, 42.49, 39.94, 39.62, 37.42, 36.80, 36.53, 35.43, 35.35, 35.03,34.76, 33.90, 33.52, 33.11, 30.68, 29.76, 27.83, 23.88, 22.41, 21.22,20.83, 17.97, 12.55, 12.13, 11.83, 11.78, 11.40.

EXAMPLE 5 Synthesis of 3-Spiro[1,3]Dioxolane-6-Oxo-Cholan-24-Oic Acid ofFormula (VI) with R_(a)═H; R₁ and R₂ Taken Together Form a —(CH₂)_(n)-Chain, wherein n is 2.

3-spiro[1,3]dioxolane-6-oxo-5β-cholan-24-oic acid methyl ester offormula (VI) (11.0 g, 24.6 mmol), as prepared as in Example 3, isdissolved in 22 mL of MeOH in a 100 mL three-neck flask comprising adropping funnel, a thermometer and a magnetic stirrer. The mixture iscooled down to 0° C. and treated with a solution of 30% of NaOH (11 mL).The reaction mixture is stirred for 18 hours at room temperature, thencooled down to 0° C. and treated with HCl 37% until reaching a pH of 2.The methanol is evaporated under reduced pressure, the aqueous phase isextracted with CH₂Cl₂ and the organic phase dried over anhydrous Na₂SO₄and concentrated to residue. 3-Spiro[1,3]dioxolane-6-oxo-cholan-24-oicacid of formula (VI) (10.9 g, 24.0 mmol) is obtained in a quantitativeyield.

¹H-NMR (CDCl₃, 200 MHz, 24° C.) δ: 0.65 (3H, s); 0.74 (3H, s); 0.91 (3H,d, J=6.2 Hz); 1.04-2.57 (26H, m); 3.97 (4H, m).

¹³C-NMR (CDCl₃, 50 MHz, 24° C.) δ: 211.71, 180.11, 109.36, 64.56, 64.48,57.02, 56.33, 56.05, 53.84, 46.93, 43.37, 41.22, 39.82, 38.19, 36.03,35.58, 31.35, 31.22, 31.04, 30.14, 28.26, 24.29, 21.80, 18.57, 12.84,12.40.

EXAMPLE 6 Synthesis of 3-Spiro[1,3]Dioxolane-6-Ethyliden-Cholan-24-OicAcid of Formula (VII) with R_(a)=H; R₁ and R₂ Taken Together Form a—(CH₂)_(n)- Chain, wherein n is 2.

Ethyltriphenylphosphonium bromide (42.70 g, 115.1 mmol) is suspendedunder inert atmosphere in anhydrous THF (340 mL) in a 250 mL three-neckflask comprising a dropping funnel, a thermometer and a mechanicalstirrer. The mixture is cooled down to 0° C. and t-BuOK (12.64 g, 113.9mmol) is added portionwise as solid and stirred for 40 minutes, thentreated with a solution of 3-spiro[1,3]dioxolane-6-oxo-cholan-24-oicacid of formula (VI) (10.9 g, 25.3 mmol), prepared as described inExample 5, in 85 mL of THF. The reaction mixture is stirred for 18 hoursat room temperature, then treated with acetic acid (8.30 g, 139 mmol).After 30 minutes of further stirring, the mixture is filtered and theobtained solution concentrated under reduced pressure. The residue isthen purified by crystallization from a solution of methanol:water 2:1.After filtration and drying3-spiro[1,3]dioxolane-6-ethyliden-cholan-24-oic acid of formula (VII)(7.50 g, 16.9 mmol) is obtained with a yield of 67%.

¹H-NMR (CDCl₃, 200 Mhz, 24° C.) δ: (diagnostic signals) 0.64 (6H, s);0.92 (3H, d, J=6.4 Hz); 1.59 (3H, d, J=6.8 Hz); 3.93 (4H, s); 4.89 (1H,q, J=6.8 Hz).

¹³C-NMR (CDCl₃, 50 Mhz, 24° C.) δ: 180.49, 139.80, 113.69, 110.32,64.50, 64.42, 56.77, 56.16, 55.07, 49.03, 43.18, 40.28, 38.09, 37.19,35.99, 35.66, 34.55, 33.73, 31.40, 31.25, 31.12, 28.45, 24.53, 21.86,18.59, 13.17, 12.50, 12.04.

EXAMPLE 7 Synthesis of3-Spiro[1,3]Dioxolane-6-Ethyliden-7α-Hydroxy-5β-Cholan-24-Oic AcidMethyl Ester of Formula (IX) with R═Me; R₁ and R₂ Taken Together Form a—(CH₂)_(n)- Chain, wherein n is 2.

3-Spiro[1,3]dioxolane-6-ethyliden-5β-cholan-24-oic acid methyl ester offormula (VII) (2.50 g, 5.46 mmol), as prepared as in Example 4, isdissolved in 15 mL of dioxane in a 50 mL two-neck flask comprising athermometer and a magnetic stirrer and the obtained solution is treatedwith SeO₂ (1.51 g, 13.6 mmol). The reaction mixture is stirred for 20hours, then diluted with 5 mL of a solution of HCl at 5% and stirred fora further hour, then filtered on celite. The solution is concentratedunder reduced pressure and diluted with 20 mL of CH₂Cl₂. The organicphase is washed with a saturated solution of NaCl and concentrated underreduced pressure. Then, the residue is purified by silica gelchromatography (CH₂Cl₂: acetone 95:5), providing3-spiro[1,3]dioxolane-6-ethyliden-7α-hydroxy-5β-cholan-24-oic acidmethyl ester of formula (IX) (1.20 g, 2.53 mmol) diastereoisomericmixture (E)/(Z) as amorphous solid with a yield of 47%.

¹H-NMR (CDCl₃, 200 MHz, 24° C.) δ: (diagnostic signals of the mixtureE/Z) 0.62 (3H, s); 0.63 (3H, s); 0.64 (3H, s); 0.77 (3H, s); 0.91 (6H,d, 6,2 Hz); 1.61 (3H, d, J=6.8 Hz), 1.65 (3H, dd, J1=7.0 Hz, J2=1.4 Hz),3.65 (6H, s); 3.92 (8H, m); 4.55 (2H, d, J=2.0 Hz); 5.05 (1H, q, J=6.8Hz), 5.50 (1H, q, J=6.6 Hz).

¹³C-NMR (CDCl₃, 50 MHz, 24° C.) δ: (mixture E/Z) 174.91, 142.30 (E),141.58 (Z), 123.97 (E), 117.29 (Z), 110.11 (Z), 109.39, 64.55, 64.46,56.02, 51.78, 50.58, 50.45, 46.31, 43.11, 42.61, 40.83, 40.37, 39.80,35.71, 33.62, 31.34, 28.45, 23.92, 22.77, 21.65, 18.60, 12.74, 12.18,12.05, 10.97.

¹H-NMR (CDCl₃, 200 MHz, 24° C.) δ: (diagnostic signals of isomer Z) 0.63(3H, s); 0.77 (3H, s); 0.91 (3H, d, 6,2 Hz); 1.65 (3H, dd, J1=7.0 Hz,J2=1.4 Hz), 3.65 (3H, s); 3.92 (4H, m); 4.55 (1H, d, J=2.0 Hz); 5.05(1H, q, J=6.8 Hz).

¹³C-NMR (CDCl₃, 50 MHz, 24° C.) δ: (isomer Z) 174.89, 141.63, 117.16,110.10 (C-3), 66.29 (C-7), 64.52 (2C), 56.02, 51.77, 50.56, 46.27,43.09, 42.58, 40.83, 39.77, 38.02, 35.71 (2C), 33.61, 31.33 (3C), 28.44,23.90, 21.65, 18.58, 12.94, 12.18, 10.96.

EXAMPLE 8 Synthesis of 3α,7α-Dihydroxy-6-Ethyliden-5β-Cholan-24-Oic AcidMethyl Ester of Formula (XI) with R_(a)═Me

3-Spiro[1,3]dioxolane-6-ethyliden-7a-hydroxy-5β-cholan-24-oic acidmethyl ester of formula (IX) (1.10 g, 2.32 mmol), obtained as describedin Example 7, and p-toluenesulfonic acid (110 mg, 0.580 mmol) aredissolved in 25 mL of a mixture of 99:1 acetone:water in a 100 mLtwo-neck flask comprising a thermometer, a reflux condenser and amagnetic stirrer. The reaction mixture is stirred for 9 hours at about25° C., then treated with 5 mL of an aqueous solution of NaHCO₃ at 5%and concentrated to residue.

The raw mixture is extracted with CH₂Cl₂ (10 mL) and the organic phasewashed with a saturated solution of NaCl (2×5 mL), dried over Na₂SO₄ andfiltered. 3-Oxo-6-ethyliden-7α-hydroxy-5β-cholan-24-oic acid methylester (X) in configuration (Z) (900 mg) is obtained after evaporation ofthe solvent under reduced pressure. NaBH₄ (53.0 mg, 1.39 mmol) issuspended under inert atmosphere in 2 mL of a mixture of THF:MeOH 9:1 at0° C. in a 10 mL two-neck flask comprising a thermometer and a refluxcondenser and the 3-oxo-6-ethyliden-7α-hydroxy-5β-cholan-24-oic acidmethyl ester of formula (X) (400 mg) is added once the formation ofhydrogen is terminated. The reaction mixture is stirred for further 3hours, then treated with 1 mL of a solution of HCl at 10% and dilutedwith 10 mL of CH₂Cl₂. The organic phase is washed with a saturatedsolution of NaCl (5 mL), dried over anhydrous Na₂SO₄, filtered andconcentrated under reduced pressure. The obtained residue is purified bysilica gel chromatography (toluene:acetone 90:10) providing 130 mg (0.30mmol) of 3α,7α-dihydroxy-6-ethyliden-5β-cholan-24-oic acid methyl esterof formula (XI) with a yield of 30%.

¹H-NMR (CDCl₃, 200 MHz, 24° C.) δ: (diagnostic signals) 0.61 (3H, s);0.64 (3H, s); 0.90 (3H, d, J=6.0 Hz); 1.65 (3H, dd, J1=7.0 Hz, J2=1.4Hz); 3.61 (1H, m); 3.64 (3H, s); 4.55 (1H, d, J=2.0 Hz); 5.05 (1H, q,J=6.8 Hz).

¹³C-NMR (CDCl₃, 50 MHz, 24° C.) δ: 174.98, 141.48, 117.53, 71.96 (C-3),66.40 (C-7), 56.09, 51.82, 50.63, 46.66, 43.51, 43.15, 40.87, 39.79,38.09, 36.82, 35.74, 33.86, 31.54, 31.37 (2C), 28.47, 23.92, 21.73,18.60, 12.97, 12.20, 11.82.

EXAMPLE 9 Synthesis of 3α,7α-Dihydroxy-6-Ethyliden-5β-Cholan-24-Oic Acidof Formula (XI) with R_(a)═H

3α,7α-Dihydroxy-6-ethyliden-5β-cholan-24-oic acid methyl ester offormula (XI), with R_(a)═Me as obtained in Example 8, (80 mg, 0.19 mmol)is dissolved in 3 mL of a mixture of MeOH:NaOH at 30% 2:1 in a 10 mLone-neck flask. The mixture is stirred for 18 hours, then acidified withaqueous HCl until reaching pH=1 and extracted several times with CH2Cl2.The obtained organic phase is dried over anhydrous Na2SO4, filtered andconcentrated under reduced pressure.3α,7α-Dihydroxy-6-ethyliden-5β-cholan-24-oic acid of formula (XI),wherein R_(a) is H, (75 mg, 0.18 mmol) is obtained as a whitecrystalline solid with a yield of 96%.

¹H-NMR (CDCl₃, 200 MHz, 24° C.) δ: (diagnostic signals) 0.65 (3H, s);0.69 (3H, s); 0.95 (3H, d, J=6.2 Hz); 1.67 (3H, dd, J1=6.8 Hz, J2=1.4Hz); 3.58 (1H, m); 4.55 (1H, d, J=0.6 Hz); 5.05 (1H, q, J=6.8 Hz).

¹³C-NMR (CD₃OD, 50 MHz, 24° C.) δ: 176.92, 142.15, 116.07, 71.33, 65.58,56.27, 50.44, 46.57, 43.30, 42.82, 41.01, 39.86, 37.79, 36.79, 35.70,33.25, 31.30, 30.97, 30.90, 28.16, 23.49, 21.53, 17.84, 11.67, 11.34,11.02.

EXAMPLE 10 Synthesis of3-Spiro[1,3]Dioxolan-(6Z)-Ethylidene-5β-Cholan-24-Oic Acid Methyl Esterof Formula (VIIa)

Ethyltriphenylphosphonium bromide (98.0 g, 0.264 mol) is suspended inTHF (650 mL) under inert atmosphere is a one liter three-neck reactorequipped with a reflux condenser, thermometer and a mechanical stirrer.The mixture is cooled down to 0° C. and treated with solid t-BuOK (29.0g, 0.258 mol) added portionwise. The suspension is stirred for 60minutes, then treated with a solution of3-spiro[1,3]dioxolane-6-oxo-5β-cholan-24-oic acid methyl ester offormula (VI) (25 g, 0.056 mol), obtained as described in Example 3, in150 mL of THF. At the end of the reaction the mixture is diluted withwater (120 mL) and the organic phase is separated and concentrated underreduced pressure. The residue is extracted with heptane (2×100 mL), thecombined organic phases are washed with water (100 mL) and concentratedunder reduced pressure. The so obtained raw material is crystallizedfrom isopropanol. After filtration and drying3-spiro[1,3]dioxolan-(6Z)-ethylidene-5β-cholan-24-oic acid methyl esterof formula (VIIa) (4.6 g, 0.010 mol) is obtained with a yield of 18%.

¹H-NMR (300 MHz, CDCl₃) δ: 5.20 (1 H, q, J=6.6 Hz), 3.98-3.88 (4H, m),3.66 (3H, s), 2.62-2.54 (1H, m), 1.04-2.4 (26H, m), 1.56 (3H, d, J=6.9Hz), 0.91 (3H, d, J=6.0 Hz), 0.81 (3H, s), 0.62 (3H, s).

EXAMPLE 11 Synthesis of 3-oxo-6-Ethylidene-5β-Cholan-24-Oic Acid MethylEster of Formula (XVa)

3-Spiro[1,3]dioxolan-6-ethylidene-5β-cholan-24-oic acid methyl ester offormula (VIIa), obtained as described in Example 10, (1.30 g, 2.83 mmol)is suspended under nitrogen in a mixture of acetone (15 mL) and HCl 5%(5 mL) in a 50 mL three-neck flask comprising a thermometer, a refluxcondenser. The reaction mixture is stirred with a magnetic stirrer atroom temperature for 6 hours, then the acetone is distilled off and theresidual suspension is diluted with H₂O (10 mL). The obtained solid isfiltered, washed with H₂O (3×10 mL) and dried under vacuum at 50° C. for4 hours. 1.18 g of 3-oxo-(6Z)-ethylidene-5β-cholan-24-oic acid methylester of formula (XVa) are obtained in quantitative yields.

¹H-NMR (300 MHz, CDCl₃) δ: 5.25 (1 H, q, J=6.6 Hz), 3.66 (3H, s),2.78-1.04 (26H, m), 1.53 (3H, d, J=6.6 Hz), 0.92 (3H, d, J=6.3 Hz), 0.88(3H, s), 0.66 (3H, s).

EXAMPLE 12 Synthesis of 3α-Hydroxy-(6Z)-Ethylidene-5β-Cholan-24-Oic AcidMethyl Ester of Formula (XVIa)

3-Oxo-6-ethylidene-5β-cholan-24-oic acid methyl ester of formula (XVa),obtained as described in Example 11, (1.18 g, 2.85 mmol) is dissolved atroom temperature and under nitrogen in a mixture of methanol (6 mL) andTHF (6 mL) in a 50 mL three-neck flask equipped with a thermometer and areflux condenser. The obtained solution is cooled down to 0° C., andNaBH₄ (0.108 g, 2.85 mmol) is added portion wise as solid. The solutionis stirred at 0° C. for 30 minutes, then poured into a solution of 1 MHCl (10 mL) at 0° C. The obtained mixture is stirred for 15 minutes andthen extracted with CH₂Cl₂ (2×10 mL). The combined organic phases areconcentrated under reduced pressure and the obtained residue is purifiedby silica gel chromatography (toluene:acetone=95:5) providing 900 of3α-hydroxy-(6Z)-ethylidene-5β-cholan-24-oic acid methyl ester of formula(XVIa) with a yield of 76%.

¹H-NMR (300 MHz, CDCl₃) δ: 5.20 (1 H, q, J=6.9 Hz), 3.54-3.72 (4H, m),2.40-1.00 (26H, m), 1.54 (3H, d, J=6.6 Hz), 0.91 (3H, d, J=6.3 Hz), 0.78(3H, s), 0.63 (3H, s).

EXAMPLE 13 Synthesis of 3α,7α-Dihydroxy-(6E)-Ethylidene-5β-Cholan-24-OicAcid Methyl Ester of Formula (XIa)

3α-Hydroxy-6-ethylidene-5β-cholan-24-oic acid methyl ester of formula(XVIa), obtained in Example 12, (0.9 g, 2.17 mmol) is dissolved indioxane (15 mL) at room temperature and under nitrogen atmosphere in a50 mL three-neck flask equipped with a thermometer and a refluxcondenser. Water (60 μl) and SeO₂ (289 mg, 2.60 mmol) are added and thereaction mixture is heated to 60° C. After stirring for 1 hour, thesolution is concentrated under reduced pressure. Then, the residue isportioned between CH₂Cl₂ (10 mL) and H₂O (10 mL), the phases areseparated and the organic phase concentrated under reduced pressure. Theso obtained raw material is purified by silica gel chromatography(CH₂Cl₂:acetone=80:20), giving 500 mg of3α,7α-dihydroxy-(6E)-ethylidene-5β-cholan-24-oic acid methyl ester offormula (XIa) with a yield of 50%.

¹H-NMR (300 MHz, CDCl₃) δ: 5.49 (1 H, q, J=6.9 Hz), 3.96-3.86 (1H, m),3.65 (3H, s), 3.56-3.44 (1H, m), 2.40-1.00 (24H, m), 1.59 (3H, d, J=6.9Hz), 0.91 (3H, d, J=6.0 Hz), 0.73 (3H, s), 0.62 (3H, s).

EXAMPLE 14 Synthesis of 3α,7α-Dihydroxy-(6E)-Ethylidene-5β-Cholan-24-OicAcid of Formula (XIa)

3α,7α-Dihydroxy-(6E)-ethylidene-5β-cholan-24-oic acid methyl ester offormula (Ma), obtained in Example 13, (500 mg, 1.16 mmol) is dissolvedat room temperature and under nitrogen in methanol (5 mL) in a 50 mLthree-neck flask equipped with a thermometer and a reflux condenser.NaOH 30% (687 mg, 5.15 mmol) is added and the reaction is carried outunder stirring for 16 hours at room temperature. The solution is thenacidified with HCl 37% to pH 1, diluted with water (10 mL) and extractedwith CH₂Cl₂ (2×5 mL). The combined organic phases are concentrated underreduced pressure and the obtained residue is purified by silica gelchromatography (CH₂Cl₂:MeOH=90:10) giving 300 mg of3α,7α-dihydroxy-(6E)-ethylidene-5β-cholan-24-oic acid of formula (XIa)with a yield of 62%.

¹H-NMR (300 MHz, CDCl₃) δ: 5.49 (1 H, q, J=6.9 Hz), 3.92-3.96 (1H, m),3.46-3.56(1H, m), 2.40-1.00 (24H, m), 1.59 (3H, d, 6.6 J=Hz), 0.92 (3H,d, 6.0 J=Hz), 0.73 (3H, s), 0.63 (3H, s).

EXAMPLE 15 Synthesis of3α-(2,2-Dimethylpropanoyl)-(6Z)-Ethylidene-5β-Cholan-24-Oic Acid MethylEster of Formula (VIIa)

3.38 g (8.11 mmol) of 3α-hydroxy-(6Z)-ethylidene-5β-cholan-24-oic acidmethyl ester of formula (XVIa), as obtained in Example 12, are dissolvedin THF (20 ml) at room temperature and under nitrogen atmosphere in a 50mL three-neck flask equipped with a thermometer and a reflux condenser.TEA (3.4 ml; 24.3 mmol) and pivaloyl chloride (2 ml, 16.2 mmol) areadded and the reaction mixture is heated to reflux. After stirring for16 hours, the solution is concentrated under reduced pressure. Then, theresidue is diluted with EtOAc (30 ml) and washed with HCl 5% (20 ml),NaHCO₃ saturated solution (20 ml) and H₂O (20 ml). The organic phase isconcentrated under reduced pressure giving 3.17 g of3α-(2,2-dimethylpropanoyl)-(6Z)-ethylidene-5β-cholan-24-oic acid methylester of formula (VIIa) with a yield of 78%.

¹H-NMR (300 MHz, CDCl₃) δ: 5.20 (1 H, q, J=6.9 Hz), 4.80-4.66 (1H, m),3.66 (3H, s), 2.40-1.00 (38H, m), 0.91 (3H, d, J=6.3 Hz), 0.79 (3H, s),0.63 (3H, s).

EXAMPLE 16 Synthesis of3α-(2,2-Dimethylpropanoyl)-7α-Hydroxy-(6E)-Ethylidene-5β-Cholan-24-OicAcid Methyl Ester of Formula (XVIIa)

0.5 g (1 mmol) of the3α-(2,2-dimethylpropanoyl)-(6Z)-ethylidene-5β-cholan-24-oic acid methylester of formula (VIIa), as obtained in Example 15, are dissolved indioxane (7.5 ml) at room temperature and under nitrogen atmosphere in a50 mL three-neck flask equipped with a thermometer and a refluxcondenser. Water (20 μl) and SeO₂ (133 mg, 1.2 mmol) are added and thereaction mixture is heated to 60° C. and stirred for 2 hour, thenconcentrated under reduced pressure. The so obtained raw material ispurified by silica gel chromatography (toluene:acetone=97.5:2.5), giving100 mg of3α-(2,2-dimethylpropanoyl)-7α-hydroxy-(6E)-ethylidene-5β-cholan-24-oicacid methyl ester of formula (XVIIa) with a yield of 20%.

¹H-NMR (300 MHz, CDCl₃) δ: 5.49 (1 H, q, J=6.9 Hz), 4.66-4.54 (1H, m),3.94 (1H, s), 3.64 (3H, s), 2.40-1.00 (37H, m), 0.91 (3H, d, J=6.30 Hz),0.75 (3H, s), 0.63 (3H, s).

EXAMPLE 17 Synthesis of3α-Hydroxy-7-Oxo-(6E)-Ethylidene-5β-Cholan-24-Oic Acid of Formula(XVIIIa) and its Conversion into Obeticholic Acid of Formula (Ia)

0.1 g (0.19 mmol) of3α-(2,2-dimethylpropanoyl)-7α-hydroxy-(6E)-ethylidene-5β-cholan-24-oicacid methyl ester of formula (XVIIa), as obtained in Example 16, isdissolved in THF (1 ml) at room temperature and under nitrogenatmosphere in a 20 mL two-neck flask. 2-Iodoxybenzoic acid (IBX) adductwith quinoline (80 mg, 0.20 mmol), prepared as disclosed inPCT/EP2016/070883, are added and the reaction mixture is heated to 50°C. and stirred for 2 hour, then filtered and concentrated under reducedpressure. Then, the residue is diluted with CH₂Cl₂ (2 ml) and washedwith HCl 5% (2 ml), NaHCO₃ saturated solution (2 ml) and H₂O (2 ml). Theorganic phase is concentrated under reduced pressure giving 105 mg ofraw material that is dissolved in methanol (2 ml) and treated with NaOH30% (0.5 ml). The solution is stirred for 48 hours, then acidified withHCl 37% until reaching pH 1 and concentrated under reduced pressure. Theobtained residue is purified by silica gel chromatography(CH₂Cl₂:acetone=95:5) giving 43 mg of3α-hydroxy-7-oxo-(6E)-ethylidene-5β-cholan-24-oic acid of formula(XVIIIa) with a yield of 53%.

¹H-NMR (300 MHz, CDCl₃) δ: 6.18 (1 H, q, J=6.9 Hz), 3.70-3.58 (1H, m),2.60-1.10 (29H, m), 1.00 (3H, s), 0.94 (3H, d, J=6.3 Hz), 0.64 (3H, s).

3α-Hydroxy-7-oxo-(6E)-ethylidene-5β-cholan-24-oic acid of formula(XVIIIa) can be converted into obeticholic acid of formula (Ia)according to known methods. For example,3α-hydroxy-7-oxo-(6E)-ethylidene-5β-cholan-24-oic acid of formula(XVIIIa) can be hydrogenated with Pd/C and hydrogen gas, e.g. accordingto the teaching of EP 1 888 614 or U.S. Pat. No. 9,238,673, and reducedwith NaBH₄ as described in Example 12 of the present invention.

Alternatively, the 3α-hydroxy-7-oxo-(6E)-ethylidene-5β-cholan-24-oicacid of formula (XVIIIa) can be converted into its C₁-C₆ alkyl esteraccording to the methods disclosed above, and then converted intoobeticholic acid of formula (Ia) by hydrogenation of the (6E)-ethylidenegroup, reduction of the 7-oxo group and deprotection of the esteraccording to known methods.

1. A compound selected from the group consisting of: a compound offormula (VII):

a compound of formula (VIIa):

a compound of formula (IX):

a compound of formula (X):

a compound of formula (XII):

a compound of formula (XIII):

a compound of formula (XV):

a compound of formula (XVa):

a compound of formula (XVI)

and a compound of formula (XVIa)

wherein R_(a) is hydrogen or an optionally substituted linear orbranched C₁-C₆ alkyl group, or an optionally substituted aryl; R_(b) ishydrogen and R_(c) is OH or O-PG, wherein PG is an alcohol protectinggroup; or R_(b) is OR₁ and R_(c) is OR₂; wherein each of R₁ and R₂,which are the same or different, is a C₁-C₆ alkyl group or R₁ and R₂taken together form a —(CH₂)_(n)- chain, wherein n is 2 or 3, whereinthe symbol

indicates that the absolute configuration of the double bond can be (E)or (Z) or a mixture thereof; and the proton H-5 of the compounds offormula (VII), (IX), (X), (XII), (XIII), (XV), and (XVI) is inconfiguration 5α or 5β or a mixture thereof.
 2. A compound according toclaim 1 selected from the group consisting of:3-spiro[1,3]dioxolane-(6E/Z)-ethyliden-5β-cholan-24-oic acid methylester; 3-spiro[1,3]dioxolane-6-ethyliden-cholan-24-oic acid;3-spiro[1,3]dioxolane-(6Z)-ethylidene-5β-cholan-24-oic acid methylester; 3-spiro[1,3]dioxolane-6-ethyliden-7α-hydroxy-5β-cholan-24-oicacid methyl ester; 3-oxo-6-ethylidene-5β-cholan-24-oic acid methylester; 3α-hydroxy-(6Z)-ethylidene-5β-cholan-24-oic acid methyl ester;3α-(2,2-dimethylpropanoyI)-(6Z)-ethylidene-5β-cholan-24-oic acid methylester; and3α-(2,2-dimethylpropanoyl)-7α-hydroxy-(6E)-ethylidene-5β-cholan-24-oicacid methyl ester.
 3. A pharmaceutical composition comprising a compoundof formula (Ia), which is 6α-ethyl-3α,7α-dihydroxy-5β-cholan-24-oicacid, also known as 6α-ethyl-chenodeoxycholic acid, obeticholic acid oras 6-ECDCA,

and a pharmaceutically acceptable carrier, wherein the obeticholic acidof formula (Ia) does not comprise chenodeoxycholic acid of formula 2


4. The pharmaceutical composition as defined in claim 3, whereinobeticholic acid of formula (Ia) is obtained starting fromhyodeoxycholic acid having the following formula (II)